Millable Fracture Balls Composed of Metal

ABSTRACT

A ball is used for engaging in a downhole seat and can be milled out after use. The ball has a spherical body with an outer surface. An interior of the spherical body is composed of a metallic material, such as aluminum. The spherical body has a plurality of holes formed therein. The holes extend from at least one common vertex point on the outer surface of the spherical body and extend at angles partially into the interior of the spherical body.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of the U.S. Prov. Appl. 61/774,729,filed 8 Mar. 2013, which is incorporated herein by reference.

BACKGROUND OF THE DISCLOSURE

In a staged fracturing operation, multiple zones of a formation need tobe isolated sequentially for treatment. To achieve this, operatorsinstall a fracturing assembly down the wellbore, which typically has atop liner packer, open hole packers isolating the wellbore into zones,various sliding sleeves, and a wellbore isolation valve. When the zonesdo not need to be closed after opening, operators may use single shotsliding sleeves for the fracturing treatment. These types of sleeves areusually ball-actuated and lock open once actuated. Another type ofsleeve is also ball-actuated, but can be shifted closed after opening.

Initially, operators run the fracturing assembly in the wellbore withall of the sliding sleeves closed and with the wellbore isolation valveopen. Operators then deploy a setting ball to close the wellboreisolation valve. This seals off the tubing string of the assembly so thepackers can be hydraulically set. At this point, operators rig upfracturing surface equipment and pump fluid down the wellbore to open apressure actuated sleeve so a first zone can be treated.

As the operation continues, operates drop successively larger balls downthe tubing string and pump fluid to treat the separate zones in stages.When a dropped ball meets its matching seat in a sliding sleeve, thepumped fluid forced against the seated ball shifts the sleeve open. Inturn, the seated ball diverts the pumped fluid into the adjacent zoneand prevents the fluid from passing to lower zones. By droppingsuccessively increasing sized balls to actuate corresponding sleeves,operators can accurately treat each zone up the wellbore.

FIG. 1A shows an example of a sliding sleeve 10 for a multi-zonefracturing system in partial cross-section in an opened state. Thissliding sleeve 10 is similar to Weatherford's ZoneSelect MultiShiftfracturing sliding sleeve and can be placed between isolation packers ina multi-zone completion. The sliding sleeve 10 includes a housing 20defining a bore 25 and having upper and lower subs 22 and 24. An innersleeve or insert 30 can be moved within the housing's bore 25 to open orclose fluid flow through the housing's flow ports 26 based on the innersleeve 30's position.

When initially run downhole, the inner sleeve 30 positions in thehousing 20 in a closed state. A breakable retainer 38 initially holdsthe inner sleeve 30 toward the upper sub 22, and a locking ring or dog36 on the sleeve 30 fits into an annular slot within the housing 20.Outer seals on the inner sleeve 30 engage the housing 20's inner wallabove and below the flow ports 26 to seal them off.

The inner sleeve 30 defines a bore 35 having a seat 40 fixed therein.When an appropriately sized ball lands on the seat 40, the slidingsleeve 10 can be opened when tubing pressure is applied against theseated ball 40 to move the inner sleeve 30 open. To open the slidingsleeve 10 in a fracturing operation once the appropriate amount ofproppant has been pumped into a lower formation's zone, for example,operators drop an appropriately sized ball B downhole and pump the ballB until it reaches the landing seat 40 disposed in the inner sleeve 30.

Once the ball B is seated, built up pressure forces against the innersleeve 30 in the housing 20, shearing the breakable retainer 38 andfreeing the lock ring or dog 36 from the housing's annular slot so theinner sleeve 30 can slide downward. As it slides, the inner sleeve 30uncovers the flow ports 26 so flow can be diverted to the surroundingformation. The shear values required to open the sliding sleeves 10 canrange generally from 1,000 to 4,000 psi (6.9 to 27.6 MPa).

Once the sleeve 10 is open, operators can then pump proppant at highpressure down the tubing string to the open sleeve 10. The proppant andhigh pressure fluid flows out of the open flow ports 26 as the seatedball B prevents fluid and proppant from communicating further down thetubing string. The pressures used in the fracturing operation can reachas high as 15,000-psi.

After the fracturing job, the well is typically flowed clean, and theball B is floated to the surface. Then, the ball seat 40 (and the ball Bif remaining) is milled out. The ball seat 40 can be constructed fromcast iron to facilitate milling, and the ball B can be composed ofaluminum or a non-metallic material, such as a composite. Once millingis complete, the inner sleeve 30 can be closed or opened with a standard“B” shifting tool on the tool profiles 32 and 34 in the inner sleeve 30so the sliding sleeve 10 can then function like any conventional slidingsleeve shifting with a “B” tool. The ability to selectively open andclose the sliding sleeve 10 enables operators to isolate the particularsection of the assembly.

When aluminum balls B are used, more sliding sleeves 10 can be useddownhole for the various stages because the aluminum balls B can have aclose tolerance relative to the inner diameter for the seats 40. Forexample, forty different increments can be used for sliding sleeves 10having solid seats 40 used to engage aluminum balls B. However, analuminum ball B engaged in a seat 40 can be significantly deformed whenhigh pressure is applied against it. Any variations in pressuring up anddown that allow the aluminum ball B to seat and to then float the ball Bmay alter the shape of the ball B, compromising its seating ability orits ability to float to the surface after use.

Additionally, aluminum balls B if left downhole can be particularlydifficult to mill out of the sliding sleeve 10 due to their tendency ofrotating during the milling operation. For example, FIG. 1C shows a mill50 inserted into a sliding sleeve's housing 20 after milling a ball Bfrom an uphole sliding sleeve. Operators use the mill 50 to mill throughall the balls B and seats 40 to gain full tubing access.

One problem with using aluminum balls B can be the long mill up timesrequired per zone. For instance, milling just one frac stage when asolid aluminum ball is used can take up to an hour. During mill up,larger aluminum balls B push through the seats as a large quartersegment S of the ball. This segment S travels down to the next seat 40and contacts the next ball B, as shown in FIG. 1C. When the mill 50reaches this sliding sleeve, the aluminum segment S and the existingball B tend to spin on each other and do not allow the mill 50 to graband mill up the components quickly. As are result, milling the seats 40and aluminum balls B can be longer than desired, which delays operators'ability to put the well in production.

Using non-metal balls may avoid the problem of longer milling timesbecause the non-metal balls break apart easier during mill up. Yet, asnoted previously, these non-metal balls may not hold the desiredoperating pressures and may not provide as many stages as can beobtained with the minimized aluminum ball and seat engagement.

The subject matter of the present disclosure is directed to overcoming,or at least reducing the effects of, one or more of the problems setforth above.

SUMMARY OF THE DISCLOSURE

A plug is used for engaging in a downhole seat and is milled out afteruse. The plug has a body with an outer surface and an interior. The plugcan be a ball, and the body can be spherical. Additionally, the plug'sbody can be composed of a metallic material, such as aluminum.

The body has a plurality of holes formed therein. In particular, theholes extend from at least one common vertex point on the outer surfaceof the body and extend at angles partially into the interior of thebody. The at least one common vertex point can be at least one tap holedefined in the outer surface of the body, and the plurality of holes canbe a plurality of angled holes formed at an angle into the interior fromthe at least one tap hole. At least a portion of the holes can have afiller material disposed therein.

In one implementation, common vertex points disposed on opposing sidesof the body can be used. In this case, the holes include a first set ofangled holes formed at an angle into the interior from one of the commonvertex points on one of the opposing sides. Additionally, the holesinclude a second set of angled holes formed at an angle into theinterior from the other of the common vertex points on the other of theopposing sides. The first and second sets of angled holes can be offsetfrom one another.

Manufacturing the plug involves forming the body with the outer surfaceand the interior. The holes are formed in the body by extending theholes from at least one common vertex point on the outer surface of thebody and extending the holes at angles partially into the interior ofthe body.

To extend the holes from the at least one common vertex point on theouter surface of the body, the method can involve forming at least onetap hole in the outer surface of the body and forming a plurality ofangled holes formed at an angle into the interior from the at least onetap hole. In one implementation, tap holes can be formed on opposingsides of the body. In this way, a first set of angled holes can beformed at an angle into the interior from one of the tap holes, and asecond set of angled holes can be formed at an angle into the interiorfrom the other tap hole. These first and second sets of angled holes canbe offset from one another.

The foregoing summary is not intended to summarize each potentialembodiment or every aspect of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a sliding sleeve having a ball engaged with a seatto open the sliding sleeve according to the prior art.

FIG. 1B illustrates a close up view of the sliding sleeve in FIG. 1B.

FIG. 1C illustrates a close up view of a mill entering the slidingsleeve of FIG. 1B.

FIGS. 2A-2C illustrate cross-sectional views of a first embodiment of ametallic ball according to the present disclosure for actuating asliding sleeve.

FIGS. 3A-3C illustrate cross-sectional views of a second embodiment of ametallic ball according to the present disclosure for actuating asliding sleeve.

FIGS. 4A-4C illustrate cross-sectional views of a third embodiment of ametallic ball according to the present disclosure for actuating asliding sleeve.

FIGS. 5A-5C illustrate cross-sectional views of a fourth embodiment of ametallic ball according to the present disclosure for actuating asliding sleeve.

FIGS. 6A-6C illustrates a detailed view of a mill entering a slidingsleeve having the metallic ball of FIGS. 3A-3C.

FIG. 7 illustrates segments or shards remaining after milling a ballaccording to the present disclosure.

FIG. 8 illustrates yet another embodiment of a metallic ball foractuating a sleeve and facilitating mill out according to the presentdisclosure.

DETAILED DESCRIPTION OF THE DISCLOSURE

Fracture balls composed of metal, and particularly aluminum, havematerial removed from the ball's interior. The removal of the materialcan be done in various ways. In general, holes can drilled to aspecified depth in the ball, but the holes do not create a through-holein the ball, as this would compromise the sealing ability of the ball.Instead, the holes create voids (not through-holes) and allow the ballto stay intact during fracturing operations. The holes in the ball alsoallow the ball to break up easier during milling operations.

As noted in the background of the present disclosure, mill out of asolid metal (aluminum) ball may cause a large segment of the ball topush through the seat before being fully milled. The partially milledsegment then travels to the next ball/seat below it. The segment andball then tend spin when the mill reaches them, which increases the millup times. However, the disclosed ball having the partial hole(s) definedtherein tends to break up into smaller pieces that allow the mill tograb them when it travels to the lower seat. Although the partialhole(s) may be beneficial for milling, the ball must still be capable ofproperly seating on the ball seat and preventing leakage and must beable to withstand the increased pressures of the fracture operations.

FIGS. 2A-2C illustrate cross-sectional views of a first embodiment of aball 100 according to the present disclosure for actuating a slidingsleeve. The ball 100 has a solid, spherical body 102 composed of ametallic material, including, but not limited to, aluminum, aluminumalloy, steel, brass, aluminum bronze, a metallic nanostructure material,cast iron, etc. The metallic material is preferably one that can befloated to the surface and can be milled if necessary. Of course, theball 100 can be composed of any suitable material, even ceramics,plastics, composite materials, phenolics, Torlon, Peek, thermoplastics,or the like.

Voids, spaces, or holes are defined in the body 102 to facilitatemilling of the ball 100 when disposed in a ball seat of a tool, such asa sliding sleeve. Because the ball 100 has the purposes of sealinglyengaging the ball seat in the sliding sleeve, the ball 100 preferably isconfigured to maintain or produce a sufficient seal with the ball seatwhen seated therein. Therefore, the voids, spaces, or holes do not passentirely through the body 102. Instead, as shown in FIGS. 2A-2C, a taphole 110 is drilled in one side of the ball's body 102. The depth ofthis tap hole 110 is preferably less than half the diameter of the ball100, although it could be deeper in a given implementation.

Drilled off at angles from the tap hole 110 are a plurality of angledholes 112—four such angled holes 112 are shown in the ball 100 of FIGS.2A-2C. The tap hole 110, although it may provide a desired void in theball's body 102, is used primarily to provide a common vertex point Vnear the surface 104 of the ball 100 from which to form the angled holes112. In this way, the multiple angled holes 112 do not tap multiplepoints on the ball's outer surface 104, which could compromise thesealing capability of the ball 100 when seated.

All the same, the tap hole 110 can be left unplugged and act as asuitable void. Alternatively, the tap hole 110 can plugged withmaterial, such as epoxy, resin, solder, plastic, rubber, the same metalmaterial as the body 102, other type of metal than the body 102, or thelike. The angled holes 112 can even be filled at least partially withfiller material that can be readily milled.

Each angled hole 112 can be angled at about 45-degrees from thecenterline of the tap hole 110, and the angled holes 112 may be offsetat about 90-degrees from one another around the tap hole 110. As withthe tap hole 110, the angled holes 112 may extend to less than themid-section of the ball's body 102, but this may vary for a givenimplementation. The ball 100 in FIG. 2A-2C essentially defines holes110/112 or voids in half the ball's body 102.

For some exemplary dimensions for the ball 100 having a diameter ofabout 3-in., the tap hole 110 can be about ⅜-in. wide and can extendabout ⅓ of the diameter (e.g., about 1-in.) of the body 102. The angledholes can be about ¼-in. wide and can extend about 1.75-in. in length.Other sized balls 100 would have other dimensions, of course. In anyevent, balls 100 having a diameter of about 2-in. or greater would bebest suited for the types of holes disclosed herein simply because ballswith smaller diameters are already easier to mill.

FIGS. 3A-3C illustrate cross-sectional views of a second embodiment of aball 100 according to the present disclosure for actuating a slidingsleeve. This ball 100 is similar to that discussed previously, but tapholes 110 a-b are defined in opposing sides of the ball's body 102. Eachtap hole 110 a-b has a plurality of angled holes 112 a-b in a mannersimilar to that discussed previously. Preferably as shown, the angledholes 112 a-b are offset from one another around the axis defined by thetap holes 110 a-b so that the opposing holes 112 a-b do not meet withone another inside the body 102. Because the tap holes 110 a-b areoffset 180-degrees on opposite sides, it is less likely that both willengage the edge of a seat when landed thereon.

As before, the tap holes 110 a-b can primarily provide common verticesVa-Vb from which the opposing angled holes 112 a-b can be formed so thatmultiple tap points do not need to be made in the ball's surface 104.The ball 100 in FIG. 3A-3C essentially defines holes 110 a-b/112 a-b orvoids throughout the interior of the entire ball's body 102. If desired,the holes 110 a-b/112 a-b can be left empty or can be filled with afiller material, such as an epoxy, resin, plastic, rubber, other type ofmetal than the body's metal, or the like.

FIGS. 4A-4C illustrate cross-sectional views of a third embodiment of ametallic ball 100 according to the present disclosure for actuating asliding sleeve. This ball 100 is similar to that discussed above withreference to FIGS. 2A-2C in that a tap hole 110 and angled holes 114 aredefined in one side of the ball 100. Rather than having four angledholes as in the previous embodiment, this ball 100 has three angledholes 114 drilled at about every 120-degrees around the tap hole 110.

In other differences illustrated, the angled holes 112 can be drilled ata shallower angle from the tap hole 110. Additionally, the ends of theangled holes 112 can extend beyond the midpoint of the ball's body 102.Thus, the angled holes 112 extend nearly to the opposing side of theball's body 102.

FIGS. 5A-5C illustrate cross-sectional views of a fourth embodiment of ametallic ball 100 according to the present disclosure for actuating asliding sleeve. This ball 100 has tap holes 110 a-b and angled holes 112a-b similar to the ball 100 in FIGS. 4A-4C and has two sets of suchholes 110 a-b/112 a-b on opposing sides of the ball 100 similar to theball 100 in FIGS. 3A-3C.

As can be seen from the various arrangements of holes in FIGS. 2Athrough 5C, the metallic ball 100 can have a plurality of holes (e.g.,112) formed or drilled partially therein. Preferably, the holes 112 donot pass entirely through the ball's body 102 and do not intersect oneanother 102. Instead, the holes 112 are made from one or more commonvertices V near the surface 104 of the ball 100 and spread out from oneanother in different directions from the common vertex V. When the holes112 are formed from two or more common vertices Va-Bb as in FIGS. 3A-3Cand 5A-5C, the opposing holes 112 a-b preferably pass between each otherin a fit pattern.

In general, the ball 100 (if solid) would have about 10× the structuralstrength required to achieve its purposes downhole. Removing materialwith the holes 110/112 could reduce the structural strength to perhaps 2to 3 times what is needed. In any event, a given ball 100 with the holes110/112 is preferably capable of withstanding at least 7,000-psi, andmore preferably 10,000-psi, without collapsing on itself. Of course, thedifferent diameters of balls and seats used and the associated materialswill govern any such variables.

FIGS. 6A-6C illustrates a detailed view of a mill 50 entering a slidingsleeve having the ball 100 of FIGS. 3A-3C. As shown in FIG. 6A, the ball100 is engaged in the seat 40. The tap holes 110 and/or angled holes 112of the ball 100 can be filled with filler material (not shown). Afterfracturing, the ball 100 may be deformed by the applied pressure in waysnot specifically shown here. For example, an outer ring may form aroundthe ball 100 where it engages the shoulder of the seat 40, and the topof the ball 100 may be compressed outward. In any event, operatorseventually run a milling tool 50 down the tubing string to mill out theball 100 and seat 40. In general, the mill 50 can use any suitable typeof bit, such as a PCD type bit.

As shown in FIG. 6B, the mill 50 engages the ball 100 and bears downagainst it. As the mill 50 rotates, the voids in the metal body 102 ofthe ball 100 allow the edges and teeth of the mill 50 to engage the ball100 so that the mill 50 can bite, grab, break, and shave away thematerial of the ball 100 more readily than found with a solid metalball. Notably, the voided ball 100 may have less of a tendency to rotatewith the rotation of the mill 50, which typically happens with a solidmetal ball during milling operations. Also, if a portion of the ball 100remains intact, the holes 110/112 can allow the portion to be split whenthe mill 50 applies weight because the holes 110/112 create fractureplanes and points for grinding up the ball 100.

Finally, as shown in FIG. 6C, the mill 50 can eventually grind and breakup the ball into shavings (not shown) and possible chunks C that maythen fall or be pushed through the seat 40. Milling the aluminum ball Bcan take up to 10-min., depending of the motor, bit, flow rates, andweight on bit (WOB) used, as well as any environmental conditions.

Although these chunks C may pass to the next ball and seat downhole,their irregular shape and fragmented nature makes them easier to millfurther when the mill 50 reaches the next ball and seat arrangementdownhole. The chunks C and any exposed holes on the other ball createpoints of friction that can facilitate milling. As an example of whatpossible chunks C may be left of a metallic ball after milling andpassing through a seat, FIG. 7 illustrates several chunks of an aluminumball after being milled out at least partially.

Again, some of the ball remains as chunks during milling that can thenpass through the seat before the mill 50 actually grinds the entire balland seat during milling operations. Rather than producing a quartersegment of the ball B as encountered with a solid metal ball whenmilled, the voided ball 100 produces less uniform and less substantialchunks. One chunk is shown as being flat in shape and as definingremnants of the various holes (112) formed in the ball's body 102. Thismakes this chunk more susceptible to further breaking and grindingduring further milling stages. Other chunks are smaller pieces removedfrom the voided ball 100 during milling.

As an alternative to a spherical ball having holes to facilitatemilling, a metallic ball 200 as shown in FIG. 8 can also engage in aseat of a sliding sleeve, yet facilitate mill out when needed. The ball200 includes a fin or tail 206 on one end of the ball 200, which wouldcorrespond to the top of the ball 200 when deployed. The base body 202of the ball 200 is truncated, having a large portion 204 removed tobelow the sealing area 208 where the ball 200 would engage a seat'sshoulder. The tail 206 keeps the ball 200 oriented properly. Whenmilled, however, less of a spherical segment of the ball 200 would passthrough the seat to the next ball, which can avoid some of the problemsencountered during further milling stages.

Manufacture of the balls 100/200 disclosed herein can be performed in anumber of ways depending on the type of material used. For example, theballs 110/200 can be formed by casting, machining, drilling, and acombination thereof. Any holes 110/112 in the balls 110 can be formed bycasting, machining, drilling, and a combination thereof. These and othersuch manufacturing details will be appreciated by one skilled in the arthaving the benefit of the present disclosure.

The foregoing description of preferred and other embodiments is notintended to limit or restrict the scope or applicability of theinventive concepts conceived of by the Applicants. It will beappreciated with the benefit of the present disclosure that featuresdescribed above in accordance with any embodiment or aspect of thedisclosed subject matter can be utilized, either alone or incombination, with any other described feature, in any other embodimentor aspect of the disclosed subject matter.

In exchange for disclosing the inventive concepts contained herein, theApplicants desire all patent rights afforded by the appended claims.Therefore, it is intended that the appended claims include allmodifications and alterations to the full extent that they come withinthe scope of the following claims or the equivalents thereof.

What is claimed is:
 1. A plug for engaging in a downhole seat and beingmilled out after use, the plug comprising: a body having an outersurface and an interior, the body having a plurality of holes formedtherein, the holes extending from at least one common vertex point onthe outer surface of the body and extending at angles partially into theinterior of the body.
 2. The plug of claim 1, wherein the plug is aball, and wherein the body is spherical.
 3. The plug of claim 1, whereinthe body is composed of a metallic material.
 4. The plug of claim 3,wherein the metallic material comprises aluminum.
 5. The plug of claim1, wherein the at least one common vertex point comprises at least onetap hole defined in the outer surface of the body, and wherein theplurality of holes comprises a plurality of angled holes formed atangles into the interior from the at least one tap hole.
 6. The plug ofclaim 1, wherein the at least one common vertex point comprises commonvertex points disposed on opposing sides of the body.
 7. The plug ofclaim 6, wherein the plurality of holes comprises: a first set of angledholes formed at angles into the interior from one of the common vertexpoints on one of the opposing sides; and a second set of angled holesformed at angles into the interior from the other of the common vertexpoints on the other of the opposing sides.
 8. The plug of claim 7,wherein the first and second sets of angled holes are offset from oneanother.
 9. The plug of claim 1, wherein at least a portion of the holescomprise a filler material disposed therein.
 10. A method ofmanufacturing a plug for engaging in a downhole seat and being milledout after use, the method comprising: forming a body having an outersurface and an interior, forming a plurality of holes in the body byextending the holes from at least one common vertex point on the outersurface of the body and extending the holes at angles partially into theinterior of the body.
 11. The method of claim 10, wherein the plug is aball, and wherein the body is spherical.
 12. The method of claim 10,wherein the body is composed of a metallic material.
 13. The method ofclaim 12, wherein the metallic material comprises aluminum.
 14. Themethod of claim 10, wherein extending the holes from the at least onecommon vertex point on the outer surface of the body comprises formingat least one tap hole in the outer surface of the body,
 15. The methodof claim 14, wherein extending the holes at angles partially into theinterior of the spherical body comprises forming a plurality of angledholes formed at angles into the interior from the at least one tap hole.16. The method of claim 10, wherein extending the holes from the atleast one common vertex point on the outer surface of the body comprisesforming tap holes on opposing sides of the body.
 17. The method of claim16, wherein extending the holes at angles partially into the interior ofthe body comprises: forming a first set of angled holes at angles intothe interior from one of the tap holes; and forming a second set ofangled holes at angles into the interior from the other tap hole. 18.The method of claim 17, wherein the first and second sets of angledholes are offset from one another.
 19. The method of claim 10, furthercomprising filling at least a portion of the holes with a fillermaterial.
 20. A plug for engaging in a downhole seat and being milledout after use, the plug comprising: a body having an outer surface, atop end of the body having a fin disposed thereon, and a bottom end ofthe body opposite the top end having a sealing area on the outersurface, the bottom end being truncated below the sealing area.